Rotary radial piston machines with tangential balancing recesses for the pressure balance of the pistons



6 1 0 m I" e 5 mm 5 m .r 2 C t June 1966 K. EICKMANN ROTARY RADIAL PISTON MACHINES WITH TANGENTIAL BAL RECESSES FOR THE PRESSURE BALANCE OF THE PISTO 1963 3 S1" INVENTOR. KARL E/OKMANN WM W0 W Filed June 5,

June 14, 1966 K, E|KMANN 3,255,7U6

ROTARY RADIAL PISTON MACHINES WITH TANGENTIAL BALANCING RECESSES FOR THE PRESSURE BALANCE OF THE PISTONS Filed June 5, 1963 3 Sheets-Sheet z INVENTOR. KARL E/CKMANN 9 WW MM My June 14, 1966 E M 3,255,706

ROTARY RADIAL PISTON MACHINES wITH TANGENTIAL BALANCING RECESSES FOR THE PRESSURE BALANCE OF THE PISTONS Filed June 5, 1963 3 Sheets-Sheet 3 90 GRADE TURNED SHOWN INVENTOR Fi 8 KARL E/CKMA NN BY mu (AA W6 W MWW United States Patent ROTARY RADIAL PISTON MACHINES WITH TAN- 15 Claims. in. 103-161) This invention relates to rotary fluid machines of the type including pistons reciprocable in radially extending cylinders in a rotor to vary the effective volumes of the cylinders inwardly of the pistons. More particularly, the present invention is directed to rotary fluid machines of this type including novel means for the selective utilization of pressure fluid to balance or compensate forces acting tangentially on the pistons during their reciprocation.

Machines of the type to which the present invention is directed have been used as hydraulic pumps, motors, transmissions or the like, and further as pneumatic machines and motors, rotary compressors, rotary steam motors, rotary combustion engines and the like.

In known rotary fluid machines, a rotatable rotor is formed with a plurality of angularly spaced radially extending bores constituting cylinders, and pistons are reciprocated in these cylinders, during operation of the machine under power, to vary the effective volumes of the cylinders radially inwardly of the pistons. A simple rotary fluid machine of this type, able to operate under either low pressure or high pressure and having a very high efficiency and output in comparison with its overall dimensions, is shown and described in my copending allowed U.S. patent application Serial No. 229,644, filed October 10, 1962.

Known radial piston rotary fluid machines have the disadvantage that the pistons, during their radial reciprocation, are subjected to a force component in a.tangential direction. This results in increased friction between the outer surfaces of the piston and the inner surfaces or inner cylinder wall along which the piston is reciprocated during power operation of the machine.

An object of the present invention is to provide a rotary fluid machine of the type mentioned in which the force components acting tangentially on the pistons during radial reciprocation thereof are compensated or balanced to reduce the friction between each piston and its associated cylinder wall, thereby to increase the overall efiiciency of the machine as well as the overall power output.

Another object of the invention is to provide, in rotary fluid machines of the type mentioned, recess means between the outer surfaces of the pistons and the inner surfaces of the associated cylinders and means for supplying fluid under pressure selectively to these recesses to balance or compensate force components acting tangentially on the pistons during reciprocation thereof when the machine is operated under power.

A further object of the invention is to provide, in rotary fluid machines of the type just mentioned and having such balancing recesses, means for selectively applying such fluid pressure in accordance with the tangential direction in which such force components are then acting.

Yet another object of the invention is to provide such balancing or compensating means for force components acting tangentially on pistons reciprocating radially in the cylinders of a rotor in a simple and eflicient manner.

Still a further object of the invention is to provide such compensating or balancing means, for forces acting tangentially on radially reciprocated pistons, in a piston and guide shoe assembly of simple and inexpensive design.

In my said copending U.S. patent application Serial No.

provided in the cylinder wall.

Patented June 14, 1966 229,644 I have disclosed piston and guide shoe assemblies, in rotary fluid machines, in which the guide shoes are co operable with rotary guide rings and rotary support rings. The guide shoes are shown as having radially outwardly facing recesses in their radially outer guiding faces, together with means for supplying fluid under pressure to such recesses from the associated cylinders through the respective pistons. Thereby radially inwardly directed forces against the guide shoes are counterbalanced so that the piston and guide shoe assemblies travel along the rotating ring and guide ring means with greatly decreased friction.

From rotary fluid machines, it is known that, during rotation of the rotor, the piston guide means have a certain pivoting or oscillatory movement about their connection axes to the pistons, with these connection axes extending parallel to the rotor axis. This pivoting or oscillatory movement is due to the eccentricity between the axis of the rotor and the axis of the rotary guide ring means. It is this oscillatory or pivotal movement which produces a force component acting in a generally tangential direction on the pistons and substantially normal to the piston axes. act either in the direction of rotation of the rotor or in the opposite direction.

However, in either case, the piston is pressed by such force components against the cylinder wall along which the piston is reciprocating. This results in increased friction between the piston and the cylinder wall, and this friction increases with the degree of relative pivoting of the piston guide means. The friction reduces the overall efiiciency and power output of the machine. To date, no effective means has been suggested for decreasing this particular friction component.

In accordance with the invention, the recess means to which the fluid under pressure is supplied to compensate the tangential force components may be provided either in the cylinder wall or the piston wall, but preferably are Preferably, two diametrically opposite recesses are provided in the exterior surface of the piston, these recesses being centered with respect to a diametric plane through the rotor and the associated piston. In addition, the supply of fluid under pressure to one or the other or to both of these recesses is effected under the control of the piston guide shoes, and particularly responsive to the direction and amplitude of the relative oscillatory movement of the piston guide shoes. The fluid under pressure is supplied to the balancing recesses only when the guide shoe pivots out of its normal position, and is supplied only to that recess which then is located in the direction in which the tangential force com.- ponent is acting. Consequently, when there is a tangentially acting force component perpendicular to the piston axis, the force of the fluid under pressure acting in such recess is substantially proportional and substantially in opposition to the tangential force component transmitted from the connected piston guide shoe, or from the driving or drive mechanism to the respective piston. Thus, the force component acting on the piston in a direction tangentially of the rotor is partially or completely balanced by the force of the fluid pressure in'the respective tangential recesses.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a longitudinal sectional view, essentially corresponding to a diametric plane through an associated rotor, of one embodiment of piston and piston guide shoe assembly in accordance with the invention;

FIG. 2 is a view, similar to FIG. 1, of another embodi- Such tangential force components may ment of a piston and guide shoe assembly in accordance with the invention;

FIG. 3 is a sectional view, corresponding to a diametric plane through an associated rotor, of the piston guide shoe shown in FIG. 1;

FIG. 4 is an elevation view corresponding to FIG. 3 and looking in the direction of the arrow IV;

FIG. 5 is a top plan view of the guide shoe shown in FIGS. 3 and 4;

FIG. 6 is a longitudinal sectional view, corresponding to FIG. 1, but showing the piston per se;

FIG. 7 is an elevation view corresponding to FIG. 6 taken in the direction of the arrow VII;

FIG. 8 is a longitudinal or axial sectional view through a rotary fluid machine incorporating piston and guide shoe assemblies embodying the invention; and

FIG. 9 is a sectional view through FIG. 8 taken along the line IX-IX.

In the drawings, a relatively elongated and substantially circular cross section piston 1 is illustrated as having a relatively small diameter bore 8 extending axially therethrough and intersecting a relatively large diameter bore 23 extending diametrically of piston 1 adjacent its radially outer end and opening through this radially outer end. Bore 23 receives the cylindrical trunnion 4 of a piston guide shoe having a central member 2, which is arcuate in cross section, extending in parallel relation to the axis of trunnion 4 and in outwardly spaced relation to this trunnion. Circumferentially extending arcuate wings 3 are provided at opposite ends of central member 2, and the latter is formed with a radially outwardly opening recess 6 in its outer end communicating with a relatively small diameter bore or passage 7 extending radially of trunnion 4.

Referring particularly to FIGS. 1, 2, 6 and 7, the cylindrical surface of piston 1 adjacent the radially outer end thereof, is formed with a pair of diametrically opposite recesses 10 and 12 facing in opposed directions considered with respect to the direction of circumferential movement of piston 1. Recess 10 may be considered the forward or leading recess, whereas recess 12 is the rearward or trailing recess, again considered from the direction of rotation of a rotor in which piston 1 is mounted. A channel or bore 9 interconnects leading recess 10 and bore 23, and a channel or bore 11 interconnects trailing recess 12 and bore 23. Bores 9 and 11 extend radially of piston 1 and slope radially outwardly of the piston toward the axial inner end of the piston.

The external cylindrical surface of piston 10 is also formed with a pair of diametrically opposite limiting recesses or closed channels and 21. Channel 29 surrounds, in spaced relation, recess 10, whereas channel 21 surrounds, in spaced relation, recess 12. Generally radially extending bores or passages 18 connect recesses 20 and 21 with bore 23. Bores 19 extend inwardly from the outer end of piston 1 and communicate with respective channels 18. The bores 19 may be termed unloading channels, and provide communication between bores 18 and a space which is more or less at atmospheric pressure. This assures excessive pressure accumulating in bores 18 and limiting channels or recesses 20 and 21.

Referring particularly to FIGS. 1 through 5, trunnion portion 4 of the piston guide shoe is formed with an outwardly opening arcuate cross section recess extending longitudinally thereof and parallel to the axis thereof, this recess 5 being centered with respect to the bore or passage 7. Recess 5 is hereinafter called control recess because it differs, in function, from a somewhat similar recess shown in one of my copending applications and described as a pivot shoe inner recess, but which has been intended for an entirely different purpose. Recess 5, in its control action, cooperates with axial bore 8 and with bores or channels 9 and 11. The relative spacing of bores 9 and 11, circumferentially of bore 23, with respect to the arcuate extent of bore 5 is so selected that, in the position of the parts illustrated in FIG. 1, recess 5 is in communication with central or axial bore 8, but the solid portion of trunnion 4 prevents communication between recess 5 and channels 9 and 11. Control adjusting recesses, in the form of triangular or other cross section grooves, may be provided in the arcuate surface defining the recess 5. i

If the guide shoe pivots clockwise, for example, and as shown in FIG. 2, recess 5 establishes communication between axial passage 8 and bore 11 communicating with trailing recess 12 in the outer surface of piston 1. In this arrangement, the fluid under pressure in the cylinder beneath the radial inner end of piston 1, and acting radially outwardly against the inner end of piston 1 is designated as the inner pressure field 15. This fluid under pressure communicates, through axial bore 8, control recess 5 and channel 11 with the trailing recess 12. If guide shoe 2 pivots counterclockwise, or to a position substantially opposite to that shown in FIG. 2, control recess 5 would connect passage 8 through channel 9 to the leading recess 10 in the outer surface of piston 1. Thus, the radially inner pressure field 15 would be effective in the leading recess 10.

In the embodiment of the invention shown in FIG. 2, control recess 5 is not provided with the adjusting grooves 22. Consequently, communication between axial bore 8 and channels 9 or 11 occurs abruptly or is interrupted abruptly during pivoting or oscillation of the guide shoe. Contrary thereto, in the embodiment of FIG. 1, the control adjusting grooves provide for a gradual establishment of communication or interruption of communication between passage 8 and a channel 9 or 11 so that, with increasing relative angular displacement of the piston guide shoe, the degree of communication increases proportionately. The size and location of the grooves 22 have an influence on the effectiveness of the communication, depending upon the relative angular displacement of the piston guide shoe.

Referring again to FIGS. 1, 3, 4 and 5, arcuate cross section control ports or recesses 16 and 17 are formed in the exterior surface of trunnion member 2, and are spaced a limited angular distance from control recess 5 and adjusting grooves 22. When the guide shoe is in the position of FIG. 1, or in a substantially central position, then control ports 16 and 17 establish communication between bores 18 and passages 9 or 11, respectively. When this communication is established, low pressure or atmospheric pressure is present in the leading recess 10 and the trailing recess 12 by virtue of the passages 19 opening through the radially outer end of piston 1. If guide shoe 2 pivots in the clockwise direction, control recess 5 establishes communication between axial passage 8 and channel 11 and thus with the trailing recess 12 as already described and, during this time, control port 16 is displaced so that it is in communication only with passage 9 but not in communication with passages 18 and 19. However, control passage '17 is in communication with passages 18 and 19 :but is blocked from communication with passage 11. The reverse occurs when guide shoe 2 pivots in a counterclockwise direction.

The guide shoe per se is shown separately in FIGS. 3, 4 and 5, whereas cylinder 1 per se is shown separately in FIGS. 6 and 7. It should be noted that the provision of two balancing recesses 10 and 12, two channels 9 and L1, two control adjusting grooves 22, and two pressure unloading or equalizing channels 19 is by way of example only. Instead of providing only two of each of these means, it is possible to provide a plurality or more than two of each of such means. If required by design or other considerations, it is also possible to provide only one of the described means instead of two. However, in such an instance, only one of the recesses 10 or 12 could be effective.

In the embodiment of the invention shown in FIG. 2, communication bores 18 and channels 19 are eliminated, as well as the control ports 16 and 17 and the control grooves 22. Thus, the piston 1 and associated guide shoe 2:22 of FIG. 2 are of a very simple, practical and inexpensive design. This arrangement can be used in all practical applications where the additional means shown in FIGS. 1, 3, 4 and 5 are not required.

Arrows 13 illustrate the tangential force component resisting or acting on the piston l, and arrows 14 illustrate the radially outer pressure field acting on the guide shoes. 'During pivoting of the guide shoes, fluid under pressure passes from inner pressure field through axial passage 8 into control recess 5, and from control recess 5 through guide shoe passage 7 into recess 6 in the outer surface of shoe 7, and also through channel 11 into the trailing recess 12. The fluid, if under pressure, creates, on the piston and guide shoe assembly, the radially outer pressure field 14 in the recess 6, the tangentially acting pressure field d3 in the recess 12, and the radially inner pressure field 15 on the inner end of piston 1. The pressure forces acting in fields I4 and 115 may be substantially equal and in opposition, and thereby balance each other partially or wholly. In the relatively angularly displaced position of the guide shoe, pressure field 614 provides a radially inwardly directed component and a tangentially directed component of force to the piston and guide shoe assembly. The force of the tangentially directed field 13 acts in the direction opposite to the component of force from the radially outer pressure field of the angularly displaced guide shoe. The arrows show the direction of the resulting forces from the pressure fields 13, 14 and 15 acting against piston I and its associated piston guide shoe.

FIGS. 8 and 9 show the incorporation of the piston and guide shoe assemblies just described in a rotary fluid machine, the trailing recess I2, the control recess 5 and a narrow radially outwardly extending portion 6th of a rotor 36 being clearly illustrated. The machine shown in FIGS. 8 and 9 includes an outer casing 23 and an eccentricity adjusting means 24, 25, 27 and 29 which can be adjusted radially of casing 23. A rotating ring is supported on rotatable support rings 36 which are, in turn, rotatably mounted in anti-friction bearings 35. Ring 29 has a radially inner cylindrical surface engaging the radially outer cylindrical surface of the guide shoes and the wings 3 thereon. A shaft is provided, and rotor 30 may be coupled or clutched to this shaft. A control body may extend axially of the outer casing and retatably support the rotor 30, as by means of an interposed bushing. This control body may be formed with fluid passages 32 and 33 for flow of fluid into and out of cylinders 34 of rotor 39.

The functioning of the balancing recesses 10 and 12 and of the cooperating control recess 5 is clearly visible in FIG. 9. If the rotor is moving in a clockwise direction as viewed in FIG. 9, and if adjusting device 27 is adjusted to be eccentric in a downward. direction, then the guide-shoes in the right side of FIG. 9 are swung counterclockwise. This establishes communication between the respective cylinders 34 and their respective leading recesses 16 through the piston axial passages 8-, the trunnion control recesses 5, and the communicating channels 9 of each of the pistons 1. Thus, the pressure effective in pintle passage 33 is also effective in recess It), acting directly against the associated cylinder wall in roller 30. If, in these positions, the rotary fluid machine is acting as a motor, the fluid pressure directly forces rotor 30 to rotate. In the case of the perfect design, the force of the fluid acting radially inwardly of a respective cylinder 34 against the radially inner end of the respective piston 1 form the radially inner pressure field acting in radially outwardly direction against the piston I. At the same time, communication is effected between passage 8, control recess 5, guide shoe passage 7 and guide shoe recess 6, thereby creating the radially outer pressure field 14. The inwardly acting force of the fluid under pressure in field l4 acts substantially radially inbetween fields of fluid under pressure.

6 w-ardly against guide shoe 2 and, if guide shoe 2 is in an angularly displaced position, this force has a certain component acting tangentially in the then effective recess 10 or 12. Thus, if the design and the action of the recesses It) and 1 2 are perfectly designed, the friction under load between guide shoe 2, the adjacent guide member parts and guide member faces on the rotary guide means 29 and/ or 36, as well as the friction between piston 1 and the inner wall of a cylinder 34, are very substantially reduced if not entirely prevented. Consequently, the piston-guide shoe assemblies are partially or entirely floating between "beds of fluid forces acting from the radially outer pressure field 14, the radially inner pressure field I5 and in the respective balancing recess 10 or 12. Thereby mechanical contact, friction and sliding forces under load between adjacent surfaces are reduced or essentially pre- Vented.

The guide shoes on the left side of FIG. 9 are angularly displaced in a clockwise direction, thereby connecting the spaces in cylinder 34 inwardly of the pistons with their respective trailing recesses 12, through the mentioned passages. Thus, the pressure in pintle passage 32 acts in recesses 12 of these pistons on the left side of FIG. 9. As each piston moves past the dead center position, the associated guide shoe moves through its central position thereby preventing any communication between the recesses 10 and 12 while maintaining communication with recess 6. Thus, at a certain angular displacement before either of the dead center positions, communication between each cylinder 34 and the respective recess 10 or'll2 is interrupted while, at a certain angular displacement following either of the dead center positions, communication between each cylinder 34 and the opposite recess 12 or 10 is established. Consequently, and irrespective of whether or not the fluid machine is operating as a pump, compressor, or motor, during each revolution under power, and with adjusting de vice 27 in eccentric position, each recess 10 or 12 is, during a part of each revolution, in communication with the associated cylinder 34 and thus with one of the pintle passages 32 or 33. During another part of each revolution, each recess 19 or 12 is in communication with the other pintle passage 33 or 32. As a result, the rotary fluid machine shown in FIGS. 8 and 9 operates with greatly reduced friction, reducing wear on the parts, and with floating of the piston and guide shoe assemblies The result is the provision of a high efficiency and a useful long life of the machine.

In accordance with the invention, the tangential components of the forces acting against the piston to force the same against the inner wall of the associated cylinder is transmitted by fluid forces whereas, in prior art machines, such transmission of forces has been by mechanical contact between the pistons and the cylinders. In other words, the transmission of the tangential force components by mechanical contact is replaced, in the present invention, by fluid transmission. With perfect design, the pistons will float between fields of liquids or gases under pressure.

The application of the fluid pressure balancing principles has been shown, by way of example only, in a particular embodiment of rotary fluid machine as illustrated in FIGS. 8 and 9. However, it should be understood that the fluid balancing principle is applicable to other types of'rotary fluid machines having pivotally or swingably mounted piston guide shoes. Also, the particular type of piston guide shoe pivotally mounted upon the piston is of no limiting consequence to the fluid balancing principles of the present invention.

Another very important feature of the invention should be noted. This is the fact that the guide shoes pivotally connected to the pistons absolutely prevent relative rotation of the pistons and their axis. This is due not only to the guiding engagement of the guide shoes with the guide means shown in FIGS. 8 and 9 but also due to the arcuate configuration of the guide shoes engaging the inner cylindrical guiding surfaces on the guide means. The reasons for such prevention of axial rotation of the piston by virtue of the construction of the guide shoes and the interrelated and eccentric guiding means will be clearly apparent from a consideration of FIG. 8 and the action of the guide ring 9 and the associated support rings 36 on the guide shoes.

While specific embodiments of the invention have been shown and described to illustrate the application of the principles of the invention, it should be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A rotary fluid machine comprising, in combination, a casing; a body formed with angularly spaced radial bores constituting cylinders; means mounting said body in said casing for movement relative thereto; pistons reciprocable in said cylinders to vary the effective volumes of said cylinders to displace fluid relative to said cylinders; piston guide shoes pivotally connected to the ends of said pistons for pivoting about axes substantially parallel to each other and perpendicular to the axis of the respective cylinder, said guide shoes having arcuate guide surface means; means restraining rotation of said pistons and said guide shoes about the axes of said cylinders; guide means in said casing having cylindrical guide surfaces substantially conformingly engageable with said arcuate guide surface means to reciprocate said pistons and said guide shoes, said guide means having an eccentricity relative to said body; said guide shoes pivoting relative to the respective connected pistons, during movement of said body, in accordance with the eccentricity of said guide means, whereby forces acting tangentially thereto are imposed on the respective pistons; the outer lateral surface of each piston and the inner surface of the associated cylinder conjointly defining at least one recess therebetween; and means selectively operable to connect each recess to the cylinder space beneath the associated piston to supply fluid to the recess at a pressure substantially proportional to said tangential forces imposed on the respective piston, and in a direction to compensatingly oppose such forces.

2. A rotary fluid machine, as claimed in claim 1, in which said selectively operable means comprises control means operatively associated with the respective guide shoes.

3. A rotary fluid machine, as claimed in claim 1, in

which said selectively operable means comprises cooperating passage means in each piston and in the associated guide shoe, and communicating with the respective recess and with the end of the respective piston.

4. A rotary fluid machine, as claimed in claim 3, said selectively operable means further including control means operable periodically during movement of said body to open and close said passage means.

5. A rotary fluid machine, as claimed in claim 1, in which there are a pair of recesses with respect to each piston, the pair of recesses being located at opposite ends of a diameter of the associated cylinder, one recess facing in a leading direction with respect to movement of said body and the other recess facing in a trailing direction with respect to movement of said body.

6. A rotary fluid machine, as claimed in claim 5, in which said selectively operable means includes a passage extending longitudinally of each piston and opening through the end of the latter, and further includes a control means for' each piston and guide shoe combination, eltective, during movement of the body, to connect one recess at a time to the associated piston passage.

7. A rotary fluid machine, as claimed in claim 1, in which each recess is formed in the outer lateral surface of the associated piston and is closed by the inner surface of the associated cylinder.

8. A rotary fluid machine, as claimed in claim 1, in which said selectively operable means connects each recess to the associated cylinder space during one part of a complete stroke of the respective piston, and disconnects each recess from the associated cylinder space during the remainder of each complete stroke of the associated piston.

9. A rotary fluid machine, as claimed in claim 1, in which the pivotal connection between each guide shoe and the associated piston comprises a circular cross section bore extending diametrically of the associated piston and opening through the end thereof, and a circular cross section trunnion on each guide shoe each oscillatably engaged with a conforming fit in the associated diametric bore; each guide shoe including a portion extending radially from its trunnion and mounting the arcuate guide surface means; said selectively operable means including a passage extending substantially axially of each piston and interconnecting the other end of the piston and the diametric bore therein, and passage means interconnecting each recess to the diametric bore of the associated piston; said selectively operable means further including control means on the trunnion of the associated guide shoe and selectively operable to interconnect said piston passage and said passage means.

10. A rotary fluid machine, as claimed in claim 9, in which there are a pair of said recesses for each piston, each formed in the outer lateral surface of the associated piston and closed by the inner surface of the associated cylinder, said recesses being at respective opposite ends of a diameter of the associated cylinder, one recess leading in the direction of movement of said body and the other recess trailing in the direction of movement of said body; said control means selectively connecting one recess at a time to said piston axial passage.

11. A rotary fluid machine, as claimed in claim 10, in which said passage means comprises a pair of second passages each communicating at one end with a respective recess, the other ends of said second passages being spaced equal angular distances from said piston axial passage; said control means including a port in the trunnion of the associated guide shoe and having an arcuate extent sufllcient to connect one second passage at a time to said piston axial passage but insuflicient to connect both second passages simultaneously to said axial passage.

12. A rotary fluid machine, as claimed in claim 11, in which said port in each trunnion has an arcuate inner surface; and grooves extending from the center of said arcuate inner surface to the ends thereof, each groove increasing in depth toward the ends of the arcuate surface.

13. A rotary fluid machine, as claimed in claim 11, in which the outer lateral surface of each piston has a groove extending around and in spaced relation to the periphery of each recess, each groove being continuous; third passages each connecting a respective groove to the end of the associated piston having said bore therein; fourth passages each connecting a respective third passage to the diametric bore of the respective piston; and a pair of second control ports on the trunnion of each associated guide shoe each selectively operable to connect a second passage to a fourth passage, in accordance with the relative angularity of the associated guide shoe, to connect the associated groove to that end surface of the associated piston having the bore therein, to establish a reduced and substantially atmospheric pressure in the associated groove.

14. A rotary fluid machine, as claimed in claim 13, in which each of said second control ports is spaced an equal distance angularly from said first mentioned control port and, when the associated guide shoe is in the central position with respect to its connected piston, connecting the respective first passage to the respective fourth passage.

15. A rotary fluid machine, as claimed in claim 14, in which each second port, when the associated guide shoe is displaced angularly with respect to its connected piston,

9 10 is out of registry with the associated first passage and, in 3,106,138 10/1963 Thoma 103-462 X the opposite angular position of the associated guide shoe, 3,142,262 7/ 1964 Fifth t a1 10 2 is out of registry with the associated fourth passage. FOREIGN PATENTS References Cited by the Examiner 5 968651 6/1958 Germany' UNITED STATES PATENTS SAMUEL LEVINE, Primary Examiner.

2,604,856 7/1952 Henrichsen 103-162 LAURENCE EFNER,

2,721,519 10/ 1955 HeHliChSeH 1 -1 J. C. MUNRO, R. M. VARGO, Assistant Examiners. 

1. A ROTARY FLUID MACHINE COMPRISING, IN COMBINATION, A CASING; A BODY FORMED WITH ANGULARLY SPACED RADIAL BORES CONSTITUTING CYLINDERS; MEANS THERETO; PISTONS RECIPROCABLE IN SAID CYLINDERS TO VARY THE EFFECTIVE VOLUMES OF SAID CYLINDERS TO DISPLACE FLUID RELATIVE TO SAID CYLINDERS; PISTON GUIDE SHOES PIVOTALLY CONNECTED TO THE ENDS OF SAID PISTONS FOR PIVOTING ABOUT AXIS SUBSTANTIALLY PARALLEL TO EACH OTHER AND PERPENDICULAR TO THE AXIS OF THE RESPECTIVE CYLINDER, SAID GUIDE SHOES HAVING ARCUATE GUIDE SURFACE MEANS; MEANS RESTRAINING ROTATION OF SAID PISTONS AND SAID GUIDE SHOES ABOUT THE AXIS OF SAID CYLINDERS; GUIDE MEANS IN SAID CASING HAVING CYLINDRICAL GUIDE SURFACES SUBSTANTIALLY CONFORMINGLY ENGAGEABLE WITH SAID ARCUATE GUIDE SURFACE MEANS TO RECIPROCATE SAID PISTONS AND SAID GUIDE SHOES, SAID GUIDE MEANS HAVING AN ECCENTRICITY RELATIVE TO SAID BODY; SAID GUIDE SHOES PIVOTING RELATIVE TO THE RESPECTIVE CONNECTED PISTONS, DURING MOVEMENT OF SAID BODY, IN ACCORDANCE WITH THE ECCENTRICITY OF SAID GUIDE MEANS, WHEREBY FORCES ACTING TANGENTIALLY THERETO ARE IMPOSED ON THE RESPECTIVE PISTONS; THE OUTER LATERAL SURFACE OF EACH PISTON AND THE INNER SURFACE OF THE ASSOCIATED CYLINDER CONJOINTLY DEFINING AT LEAST ONE RECESS THEREBETWEEN; AND MEANS SELECTIVELY OPERABLE TO CONNECT EACH RECESS TO THE CYLINDER SPACE BENEATH THE ASSOCIATED PISTON TO SUPPLY FLUID TO THE RECESS AT A PRESSURE SUBSTANTIALLY PROPORTIONAL TO SAID TANGENTIAL FORCES IMPOSED ON THE RESPECTIVE PISTON, AND IN A DIRECTION TO COMPENSATINGLY OPPOSE SUCH FORCES. 